BEGIN {  # because API is called first at start, to even work when mutually recursive included
    require Exporter;
    our @ISA = qw(Exporter);
    our @EXPORT_OK = qw(message warning error output);        # symbols to export on request
    our %EXPORT_TAGS = (log => [qw(message warning error)], );
    my %seen;                                                 # code for :all tag
    push @{$EXPORT_TAGS{all}}, grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} for keys %EXPORT_TAGS;
}